<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input type="text" id="i1">
<input type="text" id="i2">
<input type="button" value="加" onclick="f1()">
<input type="button" value="减" onclick="f2()">
<input type="button" value="乘" onclick="f3()">
<input type="button" value="除" onclick="f4()">
<div>结果</div>
<script>

  let i1=document.querySelector("#i1")
  let i2=document.querySelector("#i2");
  let d=document.querySelector("div");

  function f1(){
      if (isNaN(i1.value)||isNaN(i2.value)){
          d.innerText = "输入错误!";
          return;
      }
    d.innerText="结果:"+(parseFloat(i1.value)+parseFloat(i2.value));
  }
  function f2() {
      if (isNaN(i1.value)||isNaN(i2.value)){
          d.innerText = "输入错误!";
          return;
      }
    d.innerText="结果:"+(parseInt(i1.value)-parseInt(i2.value));
  }
  function f3() {
      if (isNaN(i1.value)||isNaN(i2.value)){
          d.innerText = "输入错误!";
          return;
      }
    d.innerText="结果:"+(parseInt(i1.value)*parseInt(i2.value));
  }
  function f4() {
      if (isNaN(i1.value)||isNaN(i2.value)){
          d.innerText = "输入错误!";
          return;
      }
    d.innerText="结果:"+(parseInt(i1.value)/parseInt(i2.value));
  }
</script>
</body>
</html>